This invention pertains to archery bows, archery bow cam assemblies and methods of adjusting an eccentric profile of an archery bow cam assembly.
Various types of archery bows have been developed, including traditional bows (i.e., long bows and recurved bows) and compound bows. The archery bows include a pair of opposed limbs extending from a handle of the bow. As an archer draws the bow by pulling on a drawstring, the limbs flex and store energy. This energy is transferred to the arrow as the archer releases the drawstring.
A compound bow is a popular design for archery bows and comprises incorporating one or more cams (for example, eccentric wheels or pulleys) into the bow. These bows use a cable system which extends over at least one cam rotatably mounted at a distal end of a bow limb to provide a mechanical advantage during a draw of the drawstring (i.e., pulling back the drawstring from an initial stationary position). That is, the force required to move the drawstring (i.e., the draw force) varies as a function of the draw position of the drawstring from the initial position of the drawstring as an archer begins to pull back the drawstring to the final draw position of the drawstring where the archer holds the drawstring just before release. The draw force is initially high, reaching a peak draw force (i.e., a peak pull force on the drawstring to maintain the draw) routinely past the mid-point of a final draw position, for example; and as the drawstring approaches the final draw position, the draw force decreases.
With this arrangement, when the drawstring is in the final draw position, maximum potential energy is stored in the bow while the force required to maintain the drawstring in the final draw position is less than the maximum draw force of the bow. In short, as the drawstring is being drawn, the draw force applied to the bow increases to a maximum force and then reduces to a lower draw force at the final draw position. Accordingly, maximum potential energy is stored in the limbs without requiring maximum draw force to hold the drawstring in the final draw position. This permits the archer to maintain aim on his target prior to release for a longer period of time for a better shot. Such a draw force decrease during the draw is referred to as the xe2x80x9clet offxe2x80x9d percentage. For example, if the maximum draw force of an exemplary bow is 80 pounds, and the bow has a 65% let off percentage, then at the final draw position the draw force needed to hold the drawstring static is 35% (100%xe2x88x9265%=35%) of 80 pounds which equals 28 pounds.
A problem in the archery bow industry is different states may have different regulations requiring different let off percentages and/or one state may have different regulations regarding let off percentages for different archer bow activities carried out within the state. For example, one state may allow a maximum let off percentage for hunting and allow a different maximum let off percentage for archery competitions.
Accordingly, a goal in the archery industry is to design compound bows which provide methods for varying let off percentages.
Another goal of the archery industry is to design compound bows which provide methods for varying draw lengths. A draw length is defined as the distance from the center of a handle riser of a bow to a drawstring in a maximum draw position at the point of the drawstring where the archer""s fingers are holding the drawstring in the maximum draw position. The ability to vary draw lengths can be important to accommodate different arm lengths of an archer.
To reach either of the above discussed goals (i.e., varying let off percentages and varying draw lengths), different bows suited for the different purposes could be provided. For example, if an archer wished to have a particular let off percentage for hunting, the archer would use one bow for hunting and use another bow with a different let off percentage for another purpose. The same solution can be use for changing draw lengths. However, having several bows for different purposes is expensive. Additionally, using several bows means an archer has to become familiar with each bow for shooting accuracy, which is inefficient and difficult for most archers.
Accordingly, it would be desirable to develop bow designs and methods to vary let off percentages and draw lengths without having to use a different bow for each particular purpose.
In one aspect, the invention includes an archery bow cam assembly having a first body and a second body discrete from the first body. The first body defines a first portion of a sheave having an eccentric profile and the second body defines a second portion of the sheave. The second body is pivotally supported on the first body and is adjustably oriented relative to the first body for adjusting the eccentric profile.
In another aspect, the invention includes an archery bow having a first limb, a second limb and a handle between the limbs. At least one rotating member is rotatably joined to at least one of the limbs, and the rotating member defines a first portion of a sheave having an eccentric profile. A body discrete from the rotating member defines a second portion of the sheave. The body is pivotally supported on the rotating member and is adjustably oriented relative to the rotating member for adjusting the eccentric profile. A string extends between the first and second limbs.
In yet another aspect, the invention includes a method of adjusting an eccentric profile of an archery bow cam assembly. A first body is provided and defines a first portion of a sheave having an eccentric profile. A second body discrete from the first body is provided pivotally supported on the first body and is adjustably oriented relative to the first body. The second body defines a second portion of the sheave. The second body is pivoted relative the first body to adjust the eccentric profile.